Field of the Invention
The present invention relates to an exhaust gas heat exchanger, particularly for use in a motor vehicle, having at least one first flow channel conducting a first fluid, which is taken up in its end regions in each case in a tube sheet, having a housing, which surrounds the first flow channel, whereby the housing has an inlet opening and an outlet opening and forms a second flow channel for a second fluid, whereby a second fluid is able to flow through the housing and the second fluid is able to flow around the first flow channel, the tube sheets are inserted in the housing such that the first flow channel is sealed off from the second flow channel, having a first diffuser, which conducts the first fluid into the first flow channel, and a second diffuser, which conducts the first fluid out of the first flow channel.
Description of the Background Art
Exhaust gas heat exchangers are used in motor vehicles today to reduce the exhaust gas temperature and thereby to greatly prevent nitrogen oxide and particulate emissions. In this regard, part of the exhaust gas is branched off downstream of the internal combustion engine and then passed through a suitable exhaust gas heat exchanger.
The cooled exhaust gas is then combined with fresh air drawn in by the internal combustion engine and again supplied to the internal combustion engine. Temperatures of up to 700° Celsius occur at the inlet of the exhaust gas heat exchanger.
Exhaust gas heat exchangers are known, for instance, from DE 10 2007 011 184 A1, that include exhaust gas-conducting tubes that are inserted on both sides into plates and are connected to these, for instance, by soldering or welding and the tubes are surrounded by a housing. The exhaust gas is thereby passed into the tubes via diffusers connected to the plates. In so doing, a coolant flows through the housing, as a result of which the coolant flows around the exhaust gas-conducting tubes.
A heat transfer occurs between the exhaust gas in the tubes and the coolant flowing around the tubes, as a result of which the exhaust gas is cooled.
A disadvantage of the prior art is that sometimes boiling processes in the coolant occur in exhaust gas heat exchangers of the described type. This adversely impacts the service life of the exhaust gas heat exchanger per se and can have a negative effect on the chemical composition of the coolant. Boiling processes can occur in particular in the inlet region, because here the hot exhaust gas directly strikes the plate of the exhaust gas heat exchanger and the plate of the exhaust gas heat exchanger is in direct contact with the coolant.
Furthermore, condensation of the exhaust gas can occur on the exit side of the exhaust gas heat exchanger. The condensing condensate can enter the combustion chamber with the exhaust gas returned to the internal combustion engine and there lead to increased corrosion and further damage to individual components.